Machines used to wrap and seal articles and packages in thermoplastic film are well known in the art. Two types of machines are commonly referred to as side-sealing and lap-sealing machines. In the typical side-sealing configuration, an article or set of articles travels, typically via a conveyer belt, toward the machine. A sheet of center-folded plastic film, having two layers, is fed from a direction, which is preferably perpendicular to the direction of the conveyer. The two layers of the film are then separated such that the article is placed between the lower layer and the upper layer. On one side of the article is the center-fold, while on the other side, there is an open edge where the two layers are not attached. The machine has several sets of belts to hold and guide the film, and a side sealing mechanism, which typically comprises a heating/sealing element that fuses or welds the two layers together and a cutting element that removes the excess material. In some embodiments, the heating element serves to cut the film as well. These elements, whether a unitary element or separate components, are referred to as the heating/sealing/cutting element throughout this disclosure. Thus, as the article passes by the side sealing mechanism, this open edge is sealed by welding the two layers together, the plastic is cut and the waste is removed and discarded. At this point, the plastic film resembles a tube, with openings at both the leading and trailing ends of the article, but sealed along both sides. As the article continues to advance, an end sealing mechanism is then employed to seal the film at the leading end of the article. The article is then advanced and the end sealing mechanism then seals the film at the trailing end of the article.
Incomplete, inconsistent or sloppy welds can be problematic with these types of machines. The choice of heating/sealing/cutting element, film thickness and film speed are all factors in determining the quality of the seal. It is possible that different types of side sealing mechanisms may optimize seals for certain configurations. For example, tubular heating elements may optimize seals for high speed and/or thick films, while heated cutting blades may optimize lower speed and/or thinner films.
One potential issue associated with side sealing units is clogging or jamming. Material, such as excess film or foreign objects may be drawn into the side sealing mechanism. For heating cutting blades, the size and shape of the device is such that the material does not cause damage to the heating element. However, tubular heating elements are much smaller, and thus are prone to damage in this scenario.
Therefore, a tubular heating element which is more resistant to damage caused by foreign material drawn into the side sealing mechanism would be beneficial.